Remote sensing using transducer

Abstract

A system for determining a characteristic of an oil well includes a signal source to generate an excitation signal during a first time duration and to generate a local oscillator signal during a second time duration. The system further includes a directional coupler, and a resonator disposed in an annulus of an oil well to receive the excitation signal through the directional coupler. The system also includes a mixer to receive a resonator signal from the resonator through the directional coupler, to receive the local oscillator signal, and to generate a mixer output signal based on the resonator signal and the local oscillator signal. The system further includes a filter to filter the mixer output signal to produce an intermediate frequency signal having an intermediate frequency, and a processor to determine a pressure or a temperature experienced by the resonator based on the intermediate frequency signal and the excitation signal.

What is claimed is: 
     
       1. A system for determining a characteristic of an oil well, the system comprising:
 a signal source to output an excitation signal having an excitation frequency during a first time duration and to output a local oscillator signal having a local oscillator frequency during a second time duration that is different from the first time duration, wherein the signal source outputs the excitation signal and the local oscillator signal on a common output connection; 
 a directional coupler; 
 a resonator disposed in an annulus of the oil well to receive the excitation signal through the directional coupler; 
 a mixer to receive a resonator signal from the resonator through the directional coupler, to receive the local oscillator signal, and to generate a mixer output signal based on the resonator signal and the local oscillator signal; 
 a filter to filter the mixer output signal to produce an intermediate frequency signal having an intermediate frequency, wherein the intermediate frequency is a difference between a frequency of the resonator signal and the local oscillator frequency; and 
 a processor coupled to the signal source and that controls generation of the excitation signal and the local oscillator signal by the signal source, wherein the processor determines a pressure or a temperature experienced by the resonator in the annulus of the oil well based on the intermediate frequency signal and the excitation signal. 
 
     
     
       2. The system of  claim 1 , wherein the directional coupler is coupled to a wellhead by an electrical connection, wherein a first terminal of the resonator is coupled to a tubing of the oil well, and wherein a second terminal of the resonator is coupled to a casing of the oil well. 
     
     
       3. The system of  claim 2 , wherein the electrical connection includes a coaxial cable, where the first terminal of the resonator is in electrical communication with a shield of the coaxial cable and wherein the second terminal of the resonator is in electrical communication with a core of the coaxial cable. 
     
     
       4. The system of  claim 1 , wherein the signal source changes the excitation frequency in iterations of generating the excitation signal during the first time duration and the local oscillator signal during the second time duration. 
     
     
       5. The system of  claim 1 , wherein the processor uses a lookup table to map a value of the excitation frequency of the excitation signal to a value of the pressure or the temperature, wherein the lookup table is generated by characterizing the resonator based on a characterization pressure or a characterization temperature prior to a placement of the resonator in the annulus of the oil well. 
     
     
       6. The system of  claim 1 , wherein different values of the frequency of the excitation signal result in different amplitudes of the intermediate frequency signal at the intermediate frequency and wherein the processor compares the different amplitudes of the intermediate frequency signal at the intermediate frequency to determine a value of the excitation frequency that corresponds to the pressure or the temperature. 
     
     
       7. A method for determining a pressure in an oil well, the method comprising:
 providing, by a signal source, an excitation signal having an excitation frequency to a resonator for a first time duration, wherein the excitation signal is provided to the resonator through a directional coupler and wherein the resonator is located in an annulus of the oil well; 
 receiving a resonator signal from the resonator for a second time duration through the directional coupler; 
 providing, by the signal source, a local oscillator signal having a local oscillator frequency to a mixer during the second time duration that is different from the first time duration, wherein the signal source outputs the excitation signal and the local oscillator signal on a common output connection; 
 mixing the resonator signal and the local oscillator signal by the mixer to generate a mixer output signal; 
 filtering the mixer output signal to produce an intermediate frequency signal having an intermediate frequency, wherein the intermediate frequency is a difference between a frequency of the resonator signal and the local oscillator frequency; and 
 processing the intermediate frequency signal to determine a pressure experienced by the resonator in the annulus. 
 
     
     
       8. The method of  claim 7 , further comprising repeating the steps of providing, receiving, mixing, filtering, and processing for different values of the excitation frequency. 
     
     
       9. The method of  claim 7 , wherein processing the intermediate frequency signal includes determining whether the intermediate frequency signal is centered at a frequency that is a difference between the excitation frequency and the local oscillator frequency. 
     
     
       10. The method of  claim 7 , wherein processing the intermediate frequency signal includes using a lookup table to map the excitation frequency to a value of the pressure. 
     
     
       11. The method of  claim 7 , wherein the signal source provides the local oscillator signal to the mixer during the second time duration. 
     
     
       12. The method of  claim 7 , further comprising characterizing the resonator prior to placing the resonator in the annulus of the oil well to associate oscillation frequencies of the resonator with pressures exerted on the resonator. 
     
     
       13. The method of  claim 12 , further comprising storing the oscillation frequencies of the resonator and the pressures exerted on the resonator in a lookup table in association with each other based on the characterization of the resonator. 
     
     
       14. A method for determining a temperature in an oil well, the method comprising:
 providing, by a signal source, an excitation signal having an excitation frequency to a resonator for a first time duration, wherein the excitation signal is provided to the resonator through a directional coupler and wherein the resonator is located in an annulus of the oil well; 
 receiving a resonator signal from the resonator for a second time duration through the directional coupler; 
 providing, by the signal source, a local oscillator signal having a local oscillator frequency to a mixer during the second time duration that is different from the first time duration, wherein the signal source outputs the excitation signal and the local oscillator signal on a common output connection; 
 mixing the resonator signal and the local oscillator signal by the mixer to generate a mixer output signal; 
 filtering the mixer output signal to produce an intermediate frequency signal, wherein the intermediate frequency is a difference between a frequency of the resonator signal and the local oscillator frequency; and 
 processing the intermediate frequency signal to determine a temperature experienced by the resonator in the annulus. 
 
     
     
       15. The method of  claim 14 , further comprising repeating the steps of providing, receiving, mixing, filtering, and processing for different values of the excitation frequency. 
     
     
       16. The method of  claim 14 , wherein processing the intermediate frequency signal includes determining whether the intermediate frequency signal is centered at a frequency that is a difference between the excitation frequency and the local oscillator frequency. 
     
     
       17. The method of  claim 14 , wherein processing the intermediate frequency signal includes using a lookup table to map the excitation frequency to a value of the temperature. 
     
     
       18. The method of  claim 14 , wherein the signal source provides the local oscillator signal to the mixer during the second time duration. 
     
     
       19. The method of  claim 14 , further comprising characterizing the resonator prior to placing the resonator in the annulus of the oil well to associate oscillation frequencies of the resonator with temperatures to which the resonator exposed. 
     
     
       20. The method of  claim 19 , further comprising storing the oscillation frequencies of the resonator and the temperatures in a lookup table in association with each other based on the characterization of the resonator.